Use of wood bottom ash in cementitious materials: a review

Abstract

The search for sustainable solutions associated with cement production has drawn increasingly attention. Concurrently, agro-industrial residues are being generated more frequently and do not have an environmentally appropriate destination. Thus, one option is to use these agro-industrial residues as supplementary cementitious materials. Among these residues, wood ash generated in thermoelectric plants or in small industrial furnaces stands out. This study presents a comprehensive review on the use of wood bottom ash (WBA) in cementitious materials, addressing its characterization, microstructure, mechanical performance, durability and environmental aspects. It is concluded that there is an optimal range of values for replacing cement by WBA between 5 and 20%. The chemical characteristics are different, with a relatively higher amount of Ca and Si. The sum of iron + aluminum + silicon oxides is generally less than 70% and the loss on ignition greater than 9%. The pozzolanicity is zero or low, but depends on the presence of the amorphous phase and the surface area. The morphology is irregular, impairing the workability, and can be improved with additives. In general, processing is necessary to adjust the properties, mainly granulometry and reactivity. The setting times were divergent. Mechanical properties were impaired and porosity increased, which negatively impacts durability characteristics. The environmental assessment of the WBA cementitious product indicated it as not harmful. Considering that there might be harmful effects in the use of ash in concrete, the material should be better studied, in addition to evaluating its use in non-structural concrete and mortars that do not require high mechanical resistance.